This invention relates to a silver halide photographic material (hereafter sometimes referred to simply as a "photographic material") and, more particularly, to a photographic material that is not only enhanced in the spectral sensitivity to the red wavelength range by novel sensitizing dyes but also improved in photographic characteristics.
It is well known that certain kinds of polymethine dyes are very effective as a means of spectrally sensitizing silver halide emulsions and many types of dye compounds are described in references such as T. H. James, "The Theory of the Photographic Process", Fourth Edition, pp.194-234, 1977, Macmillan Publishing Co., Inc., New York. Requirements for these sensitizing dyes are not limited to extending the wavelength range of sensitivity of silver halide emulsions and other conditions to be met are as follows:
1) they should achieve appropriate levels of spectral dye sensitization; PA1 2) they should have a sufficient efficiency of sensitization to provide a satisfactorily high sensitivity; PA1 3) they should not cause fogging; PA1 4) they should not cause adverse interactions with other additives such as a stabilizer, an antifoggant, a coupler, a DP' scavenger and a coating aid; PA1 5) they should not experience dye desorption or desensitization even if silver halide emulsions containing them are left to stay long after application; PA1 6) they should not increase the fog density or cause desensitization even if a silver halide photographic material containing them is left to stand for a prolonged time in a hot and humid atmosphere; and PA1 7) they should not cause color contamination (or color mixing) after development as a result of diffusion from the light-sensitive layer containing them to another sensitive layer.
Various compounds have been proposed and synthesized with a view to meeting these conditions that bear great importance in the preparation of silver halide emulsions. Among those compounds, azole-ring trimethine cyanine dyes having chalcogen atoms in the ring as typified by thiacarbocyanine, oxathiacarbocyanine, selenacarbocyanine and oxaselenacarbocyanine are characterized by having preferred spectra in the red region while insuring high efficiency of spectral sensitization and they are known as principal red sensitizers. Specific examples of those dyes include: the cyanine dyes that have an alkoxy group as a substituent on the condensed ring and which are described in U.S. Pat. No. 3,615,644; the methylenedioxy-substituted thiacarbocyanine dyes that are described in U.S. Pat. No. 2,429,574; the thiacarbocyanine dyes that have a phenyl group substituted in the 5-position and which are described in U.S. Pat. No. 2,515,913; the thiacarbocyanine dyes that have a carboxyl group substituted in the 5-position and which are described in U.S. Pat. No. 2,647,050; thiacarbocyanine dyes having an alkoxycarbonyl group substituted in the 5-position as described in U.S. Pat. Nos. 2,647,051 and 2,647,052; the carbocyanine dyes that have a phenyl group substituted in the 6-position and which are described in U.S. Pat. No. 2,485,679; the saturated carboncyclic condensed thiazolocarbocyanine dyes that are described in U.S. Pat. No. 2,336,843; various other carbocyanine dyes as described in U.S. Pat. Nos. 1,846,302, 2,112,140 and 2,481,464; trimethine dyes having a substituent on methine carbon atoms as described in U.S. Pat. Nos. 2,369,646, 2,385,815, 2,484,536, 2,415,927, 2,478,366, 2,739,964, 3,282,932 and 3,384,489; anion substituted trimethinecyanine dyes as described in U.S. Pat. Nos. 2,647,053, 2,521,705, 2,072,908, British Patent 654,690 and Examined Japanese Patent Publication No. 21711/1961; and the oxathiacarbocyanine dyes that are described in British Patent 1,012,825. Some of these cyanine dyes, as used either independently or in combination with themselves, are capable of satisfying the aforementioned conditions 1)-7); however, further improvements are needed in order to satisfy the conditions required of recent versions of photographic materials, namely, higher sensitivity, a lower level of color remnant and better storage stability.